1. Field of the Invention
The present invention relates in general to an automotive air conditioner and more particularly to a driving mechanism for driving a slide type air mix door installed in the air conditioner. More specifically, the present invention relates to the air mix door driving mechanisms of a type that employs a so-called rack-and-pinion arrangement.
2. Description of the Prior Art
In order to clarify the task of the present invention, some conventional automotive air conditioners will be briefly described before describing the detail of the present invention.
One of the conventional air conditioners is of a type which comprises an intake unit through which outside/inside air is introduced, a cooler unit with an evaporator through which the air is cooled and a heater unit with a heater core through which the air is heated. As is known, the evaporator is a device set in a refrigerant circulation cooling system, through which a low temperature-low pressure refrigerant from an expansion valve flows for cooling air passing therethrough, and the heater core is a device through which a warmed engine cooling water from an operating engine flows for heating air passing therethrough. The air intake unit, the cooler unit and the heater unit are aligned in a case and mounted on a front space of a passenger room of the vehicle. However, due to the aligned arrangement of these three units, the air conditioners of this type tend to have a longer and bulky construction and thus they are not suitable for small-sized motor vehicles.
In view of the above, various compact air conditioners have been proposed and put into practical use for such small-sized motor vehicles. One of the compact type air conditioners has such a construction that the evaporator and the heater core are stood and arranged closely in a case and aligned longitudinally in a motor vehicle. For obtaining much compact construction, a measure has been proposed wherein the cooler and heater units are integrated, by which the evaporator and heater core can be positioned much closer to each other.
In operation, through the intake unit arranged at one side of the case, air is led to the evaporator to be cooled and then distributed, by means of an air mix door, to upper and/or lower air flow passages, the lower air passage having the heater core installed therein. The air mix door is of a slide door type that slides up and down in front of mouth portions of the upper and lower air flow passages. Due to usage of this slide type door, the distance between the evaporator and the heater core can be shortened. The cooled air directed to the lower air passage is heated by the heater core and led to an air mix chamber where it is mixed with the cooled air that has passed through the upper air passage. Thus, the temperature of the air mixed in the air mix chamber depends on the work position of the air mix door. The mixed air thus having a certain temperature is then distributed to various portions of a passenger room through various air blowing openings formed in the case. Usually, mode doors are provided to the air blowing openings for providing the air conditioner with a plurality of air distribution modes.
For moving the slide type air mix door in the above-mentioned manner, a driving mechanism is employed which generally comprises two racks which are provided on lateral sides of the air mix door, two gears which are rotatably held by the air conditioner case and meshed with the racks respectively and an electric actuator which drives the gears. Thus, when the electric actuator is energized for a given time, the gears are rotated by certain angles and thus the air mix door is moved to a desired work position.
However, the above-mentioned driving mechanism has the following drawback.
That is, due to the nature of the electric actuator, the output shaft of the same inevitably has a dimensional deviation of about xc2x12xc2x0 in operation angle. While, usually the driving mechanism has no means for compensating for such dimensional deviation. Thus, due to such dimensional deviation, it tends to occur that even when the air mix door has come to a terminal stop position, energization of the electric actuator still continues, that is to say, stopping of the electric actuator is not timed with arrival of the air mix door at the stop position. In this case, the electric actuator is attacked by an excessive load inevitably, and thus the life of the electric actuator and thus that of the driving mechanism becomes shortened. In order to solve this drawback, a load sensor that turns off the electric actuator upon sensing the excessive load may be employed. However, in this case, cost performance is sacrificed.
It is therefore an object of the present invention to provide an air mix door driving mechanism for use in an automotive air conditioner, which is free of the above-mentioned drawback.
That is, an object of the present invention is to provide an air mix door driving mechanism for use in an automotive air conditioner, which can protect the electric actuator even when stopping of the electric actuator is not exactly timed with arrival of the air mix door at a stop position.
More specifically, the object of the present invention to provide an air mix door driving mechanism for use in an automotive air conditioner, which can assuredly protect the electric actuator even when energization of the electric actuator continues for a while after arrival of the air mix door at the stop position.
It is another object of the present invention to provide a gear unit which is suitable for use in the air mix door driving mechanism.
According to a first aspect of the present invention, there is provided a driving mechanism for driving a slide type air mix door slidably installed in an automotive air conditioner. The driving mechanism comprises a rack connected to the air mix door; a gear unit including an input gear, an output gear and a flexible structure through which the input gear and the output gear are integrally and coaxially connected, the output gear being operatively meshed with the rack; and an electric actuator for driving the gear unit through the input gear, wherein the flexible structure of the gear unit comprises at least one circularly extending slit formed in a cylindrical wall portion of the output gear, and a bridge portion defined between opposed ends of the slit, by which the output gear and the input gear are integrally connected.